Sea level rise, earthquakes, and flying PIGs

The first major study to look at the impact of sea level rise on Christchurch and Banks Peninsula following the 2010/11 earthquake sequence projects a watery future for many parts of the city and its surrounding shorelines. The image above1 shows changes in ground elevation between 2003 and 2011 in the Christchurch region. Areas in green/blue have moved upwards by half a metre – particularly noticeable to the west of the estuary – and areas in red and yellow down, in many places along the Avon and subsidiary streams by a metre or more.

The report, Effects of Sea Level Rise on Christchurch City (pdf), by consultants Tonkin & Taylor was released last week and suggests that as a minimum planners should take into account a 1m rise in sea level over the next 100 years. Combined with the elevations changes caused by the earthquakes, this would mean significant shoreline retreats, increased flooding in many areas and the loss of hundreds of hectares of land to the sea. It’s well worth digging into the report to get the full picture, and it will make uncomfortable reading for many in the city.

Tonkin & Taylor prepared their study before the IPCC’s AR5 Working Group One report was released, and so based their SLR numbers on a literature search and the Royal Society of NZ’s 2010 paper. They suggest a “plausible upper range” of 2m over the next 100 years, with the behaviour of the West Antarctic and Greenland ice sheets in a warming world “probably the largest uncertainty in sea level rise projections”.

And now the bad news…

The Pine Island Glacier (PIG) in West Antarctica — responsible for 25% of the ice loss from the region — is now probably beyond the point of no return, committed to melt back well inland from its current position even if the local climate cools strongly. In a new study published in Nature Climate Change this week2 an international team of scientists used detailed models of the glacier and its bed, combined with field observations, to track how the ice would behave. It suggests that the PIG could contribute as much as 10mm to sea level over the next 20 years, with the potential for much more in the longer term, as one of the authors, Dr Hilmar Gudmundsson of the British Antarctic Survey points out:

“Pine Island Glacier shows the biggest changes in this area at the moment, but if it is unstable it may have implications for the entire West Antarctic Ice Sheet. Currently we see around three millimeters of sea level rise a year, and the Pine Island Glacier retreat could contribute an additional 3.5 – 10 millimeters in the next twenty years, so it would lead to a considerable increase from this area alone. But the potential is much larger. At the Pine Island Glacier we have seen that not only is more ice flowing from the glacier into the ocean, but it’s also flowing faster across the grounding line — the boundary between the grounded ice and the floating ice. We also can see this boundary is migrating further inland.”

If the PIG is already doomed to major retreat over the next century, then stability of the whole West Antarctic Ice Sheet could be threatened. Paleoclimate studies have shown that the WAIS collapsed repeatedly in earlier warm periods, though it is thought to have taken 500 – 1,000 years to melt. During the last interglacial 125,000 years ago, sea level peaked at about 6m above present with significant melt contributions likely from the WAIS and Greenland. That was with CO2 at 300ppm. We’re now nudging 400ppm.

Ice sheet behaviour in a rapidly warming world is not something we understand well, and that means that any sensible analysis of the risks of sea level rise has to consider worst cases in both the near and long term. We can get a good idea of the long term sea level rise — where the sea level will stop rising when the climate comes into equilibrium with the ice sheets — by looking at climate history. 400ppm CO2 probably means an eventual 20m of sea level rise.

In the short term — over the next few decades — unless something truly astounding happens to the WAIS or Greenland, the impacts of sea level rise are likely to be modest and manageable — at least if affected communities take the problem seriously. But when planning infrastructure that has a longer lifespan — like rebuilding a city — then the multi-metre rises we are likely to see over the next hundred years become a critical consideration. As yet there’s little sign — Tonkin & Taylor’s thorough report included — that anyone is thinking in those terms.

12 thoughts on “Sea level rise, earthquakes, and flying PIGs”

Timely post, Gareth. 3 News covered the Tonkin & Taylor report on the 9th, see here: http://www.3news.co.nz/Climate-change-warning-for-Christchurch/tabid/1160/articleID/327822/Default.aspx
This ties in neatly with Jim Salinger’s warning to Christchurch to take a meter sea level rise by the end of the century seriously, as was quite widely reported recently. With the scale of events in Australia, the media are being forced into covering climate change, although poor old ‘Mother Nature’ is still getting most of the blame.

Meanwhile the Herald this week published an opinion pieceby Chris de Freitas downplaying the risks of sea level rise and claiming undue alarmism by local authorities. He started with a current sea level rise of 1.8mm a year, frequently reiterated, and made much of local variation in sea level rise, urging a beach-by-beach approach to any regulation.

I wrote a letter to the editor, published today, pointing out that the current rate of rise is estimated at 3mm per year by NOAA and others and that the expected global sea level rise of a metre or more this century is a measure against which local variations are hardy likely to offer much compensation.

De Freitas moves seamlessly from the role of denier to that of obfuscator and delayer when it suits his purpose. He is given frequent access to the opinion pages of the Herald and I presume can count on the senior editorial staff not knowing when he is misrepresenting scientific opinion..

Bryan, I made some comments on the De Freitas article in the online comments section, pointing out the rate of increase recently is 3mm, together with a link to some source data. Words fail me with this guy.

Nigel I hadn’t caught up with the comments on the article. It was good to see yours and a few others. I notice de Freitas didn’t gather many friends around him with this one. Bryan Leyland’s “common sense” was the pits. I can still hardly believe that TV3 news roped him in as a counter to serious scientists recently.

I have been posting notes for two years on the folly of rebuilding Christchurch in the same spot with such a short life. We have the scientist and the knowledge and the advisers. Do they talk to the politicians or do the politicians ignore them?
Try this web site with the setting at one meter. http://flood.firetree.net/
We only need one meter of sea level rise and many major cities, infrastructure and farmland go underwater. The economic consequences will be huge.
Try looking at Peterborough in the UK and also Sacramento in California.

The politicians (stand fast the Greens) and the Herald will remain committed to business as usual, because that is all they know, until the waters start lapping on the steps of Parliament. Civil Defence HQ (in the basement of the Bee Hive will be inundated. And then and only then will they wake up.
There is only one chance that this senario can be changed, and that is by an awaking by the general population that AGW is real and happening now and the future is not just jockstrap and jandels on the beach, there will be unpleasant outcomes as well. When the majority wake up to the very real threats of a rapidly warming world, then they will demand that politicians take decisive action, but it’s almost already too late.
The words of the Herald and de F are very unhelpful.

Excellent Ted talk by a clearly nervous Keren Bolter of Florida Atlantic University on her mapping of sea level rise on Florida. Very good on practical effects – including coastal roads and home mortgages, insurance. The ending (from 10 minutes) is powerful, a very personal note: http://www.youtube.com/watch?v=BEhx-Q43Tfo

Sea-level rise is complicated. Not like filling a bathtub with water, I read somewhere. A variety of factors will influence how that 3mm rise will play out in different areas, ranging from coastal subsidence (sometimes due to the weight of extra water) tectonic plate movement, even the diminishing gravitational pull of the Greenland ice sheet as it melts. I’ve read that sea levels around Greenland may actually fall as the ice sheet melts because of that lessened gravity – sea level rise displaced to a couple of hundred kilometres or more away. Might his happen in the Southern Hemisphere with PIGs?
Paid shills like de Freitas cynically use that complexity to throw doubt on the science, befuddle their readers, and thus further their aim of preventing any effective action on climate change. I trust there is a special circle of Hell reserved for these liars.

I agree that its complicated. The Kapiti case is interesting, because homeowners with academic and legal credentials are bringing their expertise to bear on SLR projections that affect the value of their properties.

They seem to have employed the likes of Dr Willem de Lange, Department of Earth and Ocean Sciences, Waikato University:

The scientific and legal discussions around these sorts of cases are going to be intense – millions and possibly billions of dollars of property are at stake.

I think its time for more central government direction on the issue. A sensible government would form a standing climate change body that provided ongoing direction on this and lots of other climate related issues that are now popping up all over the place. But then again, if the government isnt inclined to do that, the lawyers will happily step in and fight it out, beach by beach.

The full Willem paper is worth a read, particularly where he provides diagrams suggesting previous estimates of coastal change have had to be revised as being too pessimistic. At the end of the paper he suggests a methodology for estimating coastal retreat:

In 2009 the Ministry for the Environment released a report Preparing for climate change – A guide for local government in New Zealand. (ME 907). In this they advocate for rules in regional and district plans that relate to managing coastal hazard risks and the effects of climate change.
Here on Waiheke Island we are finally bedding in our new district plan (Hauraki Gulf Islands) in which climate change is mentioned once! There is therefore a total reliance on Section 31 of the Resource Management Act concerning avoidance and mitigation of natural hazards to cover this issue.
Unfortunately there appears to be no work regarding the potential impact of sea level rise in the greater Auckland region and council engineers and planners do not have this risk on their radar. Thus we have coastal development on Waiheke island ranging from millionaire’s mansions to a marina that are progressing through the consent process without adequate assessment of the risks posed by climate change and sea level rise in particular.
Just like leaky buildings, if councils consent to development when best assessment guidelines provided by ME and NIWA suggest otherwise, liability must be a consideration.